Thermal Mass

As the importance of sustainability has increased, attention has focused on ways that a design can reduce a building’s carbon emissions. For framing and flooring systems, the choice between steel and concrete solutions has provided limited opportunities to influence operational carbon. There is, however, one exception – thermal mass.

Thermal mass acts as a heat sink, tempering the internal environment by reducing and delaying the onset of peak temperatures.

Benefits of thermal mass:

Keeps the building cooler in summer and warmer in winter

Helps to avoid the use of air conditioning, leading to significant reductions in carbon emissions.

How much mass is required for the best result?

Research has proven that, for a 24-hour cycle of heating and cooling, only 100mm of mass is needed to absorb excess heat – providing additional concrete mass over 100mm will not increase the amount of excess heat that the floor is able to absorb. It may, however, result in larger foundations and additional building costs.

Composite floors are generally 130-150mm thick with 70-90mm of concrete above the ribs; precast concrete units, on the other hand, are generally 200-250mm thick. As such, composite flooring solutions provide optimum thermal mass for lightweight construction. Clearly, the choice of structural system will make a difference to the weight of the floor, the size of foundations and the overall building costs.

Illustration of beneficial effect of thermal mass on internal temperatures